Background: The number of mumps cases reported in Switzerland markedly increased from 1993 to 1995 although vaccination coverage against mumps had risen steadily since the national MMR immunization program was launched in 1987. In 1991, an estimated 80% of children 27 to 36 month-old were immunized against mumps. The purpose of the present study was to assess the hypothesis that the epidemic was the consequence of a low vaccine efficacy of the Rubini strain--a mumps vaccine strain that has been widely used in Switzerland.
Methods: Vaccine efficacy was assessed by measuring secondary attack rates among immunized and nonimmunized children 16 year-old or younger who wre family contacts of cases.
Results: From February 1993 to April 1996, Geneva pediatricians reported 283 primary cases of mumps and 63 secondary cases. Estimate of vaccine efficacy was equal to 6.3% (95% CI: -45.9; 39.8) for the Rubini strain, as compared to 73.1% (95% CI: 41.8; 87.6) for the Urabe Am 9 strain, and 61.6% (95% CI: 0.0; 85.4) for the Jeryl Lynn strain, two vaccine strains of mumps that had also been used in Geneva.
Conclusion: Our study supports the hypothesis that the Rubini vaccine strain of mumps does not confer sufficient long-lasting protection against mumps.